1. Field of the Invention
The present invention relates to seats for tractors and other off-road vehicles which encounter substantial amounts of vibration and other motion, and more particularly to seats for such vehicles which are capable of undergoing attenuating movement in response to the vibration and other motion.
2. History of the Prior Art
Off-road vehicles such as agricultural tractors and similar vehicles subject the rider to a substantial amount of vibration and other motion due to the nature of the vehicle itself and particularly to the roughness and unevenness of terrain typically negotiated by such vehicles. Consequently, it is common to provide the seats in such vehicles with the ability to undergo limited attenuating movement in one or more directions to compensate for such vibrations and other motion. Many early tractor seats, for example, were constructed so as to be capable of undergoing some vertical movement. This movement was typically controlled using damping pistons and similar apparatus. Later tractor seats came to be provided with attenuating horizontal movement in addition to or in lieu of attenuating vertical movement.
An example of a seat for use with tractors and similar off-road vehicles which is capable of attenuating movement in a generally horizontal direction is provided by a co-pending application Ser. No. 960,125, filed Nov. 13, 1978 and assigned to the assignee of the present application. The seat described in that patent application is capable of attenuating fore-aft motion by an underseat arrangement which includes a plurality of bearings slidable along parallel bars. The seat is retained in a nominal position by an opposing pair of springs, and motion of the seat is damped by a piston.
Further examples of prior art seat arrangements which provide attentuating fore-aft movement are provided by U.S. Pat. No. 3,258,241 of Oswald, U.S. Pat. No. 3,100,617 of Radke et al and U.S. Pat. No. 2,932,342 of Simons et al. Shock absorption of seat movement in the fore-aft direction is described in U.S. Pat. No. 3,190,592 of Grizzle, Jr. and U.S. Pat. No. 3,100,618 of Tengler et al.
Still other examples of prior art seat arrangements permitting limited or attenuating movement are provided by U.S. Pat No. 3,245,486 of Oswald, U.S. Pat. No. 3,335,996 of Hall et al, U.S. Pat. No. 3,061,260 of Simons et al, U.S. Pat. No. 3,999,800 of Penzotti, U.S. Pat. No. 4,099,777 of Chekirda, U.S. Pat. No. 3,917,210 of Miller, U.S. Pat. No. 4,195,883 of Ronnhult et al, U.S. Pat. No. 4,128,217 of Mazelsky, French Pat. No. 742,189 of Fricard and British patent specification No. 1,303,936 of Nystrom.
The prior art seat arrangements previously described typically limit attenuating movement in a horizontal plane or direction to a single axis or direction of movement. Based on the types of motion typically encountered by the vehicle the direction may be fore-aft or lateral. As a practical matter, the vibrations and other motions encountered occur in all directions, even though they may be more severe in one direction such as fore-aft than in a lateral direction.
It would therefore be desirable to provide a seat capable of undergoing attenuating movement along more than one axis within a generally horizontal plane. Ideally, the seat should be capable of attenuating movement in any and all directions within a generally horizontal plane.
Two different arrangements which provide for attenuating movement in any direction within a generally horizontal plane are described in a co-pending application of James E. Thompson et al, Ser. No. 219,900, filed Dec. 12, 1980, and assigned to the assignee of the present application. In both arrangements an intermediate assembly is arranged so as to be capable of movement along a first axis relative to a base assembly and a seat assembly which rotatably mounts a seat is arranged so as to be capable of undergoing movement relative to the intermediate assembly along a second axis perpendicular to the first axis. Relative movements between the intermediate assembly, the base assembly and the seat assembly are damped by shock absorbers coupled therebetween and are resisted by opposing pairs of springs.
In the first arrangement described in the co-pending application of James E. Thompson et al the intermediate assembly comprises a bearing retainer plate having bearing clusters mounted therein as well as elongated slots which receive rollers rotatably mounted on an underlying base plate and an overlying plate forming part of the seat assembly. The overlying plate rotatably supports a seat mounting plate to which the seat is fastened and which is coupled through springs and shock absorbers to a central stud mounted on the base plate.
In the second arrangement described in the co-pending application of James E. Thompson et al, the intermediate assembly is made movable relative to the base and seat assemblies by different pluralities of rollers rotatably mounted within the intermediate assembly about two different pluralities of parallel axes which are perpendicular to each other. The relative movements are damped and restrained by shock absorbers and spring pairs.
The arrangements described in the co-pending application of James E. Thompson et al comprise a significant advancement over the art in their ability to provide attenuating movement in any direction within a generally horizontal plane so as to optimize operator comfort. However, there may be occasions or applications where other arrangements are necessary or desirable. In particular, it would be highly advantageous in any event, and it may become necessary in some applications, to provide a relatively thin, planar arrangement in which substantially all of the parts of the seat support are contained within a thin, compact enclosure.